IMMEDIATE RECONSTRUCTION OF MASSIVE CRANIO-ORBITO-FACIAL DEFECTS WITHALLOGENEIC AND ALLOPLASTIC MATRICES IN BABOONS

40 cranio-orbito-facial osseous defects were created in 20 adult male baboons (Papio ursinus) to test the effectiveness of an allogeneic and an alloplastic matrix implant for the functional and morphological re pair of the disassembled craniofacial complex. In each animal, one def ect was reconstructed with a craniofacial bone segment harvested from donor adult baboons, and processed so as to obtain autolysed antigen-e xtracted allogeneic (AAA) bone matrix, preserving the bone morphogenet ic protein (BMP) activity essential for bone induction. The contralate ral defect was implanted with spherical macrobeads of polymethylmethac rylate (PMMA) coated with poly-2-hydroxyethylmethacrylate (PHEMA), and sintered into a porous molded implant, replicating the structural ana tomy of the avulsed osseous segment. Histological analysis was carried out on undecalcified and decalcified bone sections prepared from spec imens harvested at 3, 6 and 12 months after surgery. In AAA bone, the morphogenetic response was characterized by vascular invasion and mese nchymal cell aggregation after partial resorption of the implanted mat rix. This was followed by bone deposition at the osteotomy interfaces and within the medullary spaces of the implanted AAA bone. Although bo ne ingrowth did occur in some PMMA/PHEMA specimens, the majority of im plants showed fibrous union at the recipient interfaces. The limited b one ingrowth may be related to narrow interconnections between larger porous spaces after chemical synthesis of the two polymeric components . Osteogenesis in AAA bone appeared consistent with osteoconductive in vasion from the viable bone at the recipient interfaces. In addition, the finding of a delicate trabecular-like bone, appositional to the ce ntral areas of the implanted matrix, suggests bone formation by induct ion.